The present invention relates generally to printing of digital images onto photographic paper, and more particularly to removable apparatus for producing photographs on photographic paper from digital images having a means for color correction.
Color and black and white photography are a popular pastime for capturing memorable moments in time. One difficulty with photography, particularly color photography, is the production of photographs having a good image clarity, or sharpness, and having correct color. Conventional printers utilize a complex and expensive optical system and projector for producing images from negatives on photographic paper. After a negative has been developed, the procedure is typically to project light through the negative and focus the image onto the photographic paper. With respect to the printer itself and disregarding the photographic paper, the optical system and the lamp house are responsible for the quality of the image. The lamp house is also responsible for the color content of the resulting photograph. In color photographic printing, the process involves projecting light which has been filtered with the use of dichroic filters to correctly manage the spectrum of light so that the characteristics of the film negative and the characteristics of the photographic paper produce a desired positive print.
This difficulty of producing photographs having good image clarity and correct color is especially exaggerated when producing photographs from digital images. Digital images may be captured by conventional digital cameras or produced from non-digitized color photographs that are subsequently digitized by standard digital photoprocessing software. Unfortunately, photographs produced from digital images are limited in sharpness and clarity because of the digitized construction of the image itself or because of the means for exposing the image on photographic paper.
Adding to the complexity and difficulty of producing clear and color correct photographs is the commercial desire to mass produce photographs at high speeds. Depending on the type of projection device, conventional printers project digital images onto photographic paper using a line-by-line application similar to a raster technique. With this type of projection method, the line-by-line application must be synchronized with the movement of the paper web in the printer and must also account for any variance from horizontal based on the movement of the paper web. Misregistration is a common problem with this technique, and the multiple alignments required to counter misregistration is very difficult to accomplish if a desired image has high resolution. Additional operational software or algorithms are required when using this line-by-line application to offset the aforementioned variance.
Various types of projectors have been used to control the transmission of light onto the negative and to the photographic film in non-digital image photographic processing. The use of a cathode ray tube (CRT) as a means for projecting digital images for the printing of photographs is popular. With CRT projectors, two problems are presented. The first problem is the persistence of the phosphors on the face of the CRT which can cause image burn or smear. The second problem is the mismatch of the color in light that is emitted from the CRT. Current CRT projection systems are unsatisfactory because of color gamut and phosphor persistence which were not designed with photographic papers in mind. For example, conventional CRT projection systems provide a wavelength of red that is too short. Light emitted from a CRT has a much different color temperature than is desired to properly match the color response of the photographic paper. Attempting to correct this mismatch through the use of filtering the light from the CRT can produce color cross-over. This cross-over can result in printed images that do not have true color. One attempt at resolving the aforementioned problems is to incorporate a series of red, blue, and green filters with the CRT. The photographic paper is exposed multiple times with light passing through each of the filters in order to provide good resolution in the resulting photograph. Unfortunately, such procedure is slow and inefficient, particularly when used in mass photograph production.
The use of liquid crystal display (LCD) technology as a means for projecting digital images for the printing of photographs has recently gained some popularity. However, LCD projectors could require substantial optical manipulation and to accomplish the same. Further there is a limitation to the resolution and its effect on the light output. Currently, filter wheels having red-blue-green pass filters are used in combination with some LCD projectors in order to generate a colored image on photographic paper. Alternatively, three light/filter sources may be used in place of a filter wheel to provide red-blue-green light that is used to generate the colored image. Use of either the aforementioned filter wheel or the three light/filter sources requires three separate exposures thereby more consumption of time, adds to the complexity of the projection device and creates a potential source of system error in the production of color correct photographs from digital images. Additionally, such light source/filter combinations only allow for the generation of a colored image onto photographic paper that approximates the image as acquired by the system, for example by digital scanning. No color correction is provided for by these light source/filter combinations.
Depending on the lamp house that is used to produce a photographic image on the photographic paper, color correction may be necessary in order to produce a photograph with good color quality. A method for analyzing color photographs is disclosed by U.S. Pat. No. 4,676,628 (xe2x80x9cthe ""628 patentxe2x80x9d). As described in the ""628 patent, the preparation of high quality prints from color negatives encounters the problem of variations in the spectral response characteristics based on particular printing paper lots and the effects of processing variables such as chemical strength, temperatures and processing times, and negative based materials. Accordingly, when a different printing paper is used for producing photographs, conventional printers must attempt to control the color content of the photographs or produce photographs having incorrect color.
What is therefore needed is a method and apparatus for creating a digital image on photographic paper and subsequent correction of color. Further needed is a digital image printer that is capable of rapidly producing digital images on photographic paper having good clarity and sharpness and correct color content. Further needed is a digital image printer having a modular controllable digital image projection device that is easily removed and easily coupled with conventional photograph printers and presents a complete image against the photographic paper without the use of a filter wheel of multiple light/filter source.
The present invention is a method and apparatus for creating a digital image on photographic paper and subsequent correction of color. The present invention provides a digital image printer that is capable of rapidly producing digital images on photographic paper having good clarity and sharpness and correct color content. Further, the present invention provides a digital image printer having a modular controllable digital image component that is easily removed and easily coupled with conventional photograph printers and presents a complete image against the photographic paper without the use of a filter wheel or multiple light/filter source.
The present invention utilizes the technology found in liquid crystal display (LCD) video projectors, digital light processing (DLP) video projectors, and direct drive image light amplifier (DILA) video projectors. This invention corrects the color content of the images to be printed. The present invention provides a method that produces true color photographs from digitized images on photograph paper. When using LCD, DLP, or DILA based imaging devices, the present invention provides the corrective means to precisely match the light. U.S. Pat. No. 4,676,628 to Asbury (xe2x80x9cthe ""628 patentxe2x80x9d) discloses a method to offset the color spectrum content of the light and is incorporated by reference herein.
Further, the present invention is compatible with the use of existing reflector imaging chips to project the entire content of an image in much the same way that the image of a negative is projected onto photographic paper. The present invention allows the conversion of a standard photographic printer, such as currently used in labs throughout the world, to be able to print digital images. For example, the present invention may be adapted to Lucht Step One""s, Lucht VP-2 and Lucht V7, which are devices made by Sienna-Lucht of Minnesota. The present invention may also be adapted to other similar type standard printers including Kodak S series printers, Nord Package Printers and Hicks type printers. Such printers are also manufactured to conform to standard photographic print paper using RA4 type processing. The present invention is not limited to the conversion of existing photographic printers but may be incorporated into a new printer using the aforementioned digital display devices.
In one embodiment, the invented digital printer includes a central processor for retrieving digital images stored on an electronic file and for creating a negative image of the digital images, a projector controller electrically connected to the central processor, a digital imaging device electrically connected to the projector controller for creating and transmitting a color corrected image, a lamp house positioned adjacent the digital imaging device for creating an optical signal and modulating the spectral content of the optical signal in accordance to a user""s instruction, a spectral content analyzer and a lamp house controller coupled to the lamp house, a lens system for focusing the color corrected image onto photographic paper, and a paper drive having a supply and take-up for providing and advancing photographic paper. The invented digital printer may further comprise a display electrically connected to the central processor for viewing the digital images, and an enclosure for housing the components of the invented digital printer.
Digital images are inverted by the central processor which in turn instructs the projector controller to activate/deactivate portions of the digital imaging device based on the inverted digital image. The lamp house comprises a conventional lamp for providing light, a light filter system positioned adjacent the lamp that is responsive to user instruction via the lamp house controller, a heat glass positioned across the path of light emitted from the lamp, a mixing tube positioned to capture the light emitted from the lamp, a neutral density filter positioned at the light exiting end of the mixing tube and a shutter positioned between the initial density filter and the imaging means. The light filter system comprises a series of filters in order to accomplish subtractive mixing of light, which uses yellow, magenta and cyan filters, or additive mixing, which uses red, blue, and green filters. When using additive mixing three lamps corresponding to the red, blue, and green filters must be used. Light is emitted from the lamp and travels through the light filter system, through the heat glass, through the mixing tube, through the neutral density filter, through the shutter when the shutter is opened, and is directed onto the imaging device.
The light emerging from the lamp house has a desired spectral content based on the combination and position of filters in the light filter system. In one embodiment of the present invention, light is reflected by the digital imaging device through the lens system and onto the photographic paper.
The lamp house controller includes a spectral content probe that is attached to the wall of the mixing tube, an analog-to-digital (A/D) converter electrically coupled with the probe, a conventional processor electrically coupled to the A/D converter, and a display and input device that are electrically coupled to the processor. The probe detects the spectral content of light traversing through the mixing tube as an analog signal which is then converted to a digital signal by the A/D converter and transmitted to the lamp house processor. The processor then determines and quantitizes the spectral content of the light traversing the mixing tube and displays such quantified spectral content to a system user on the display. In one embodiment, the processor displays such quantified spectral content in standard photographic color correction (cc) values. The user may manipulate the spectral content in standard photographic cc values of the light traversing the mixing tube utilizing the input device. Changes to the spectral content are controlled by the lamp house processor which is electrically coupled to the filter system.
Regardless of the photographic paper type, the invented digital printer allows a digital image to be printed on photographic paper and color corrected. Further, inconsistencies in the spectral content of light that may be produced by the lamp house and caused by aging of the lamp, aging of the filter system, or any other means, may be adjusted by the lamp house controller. The present invention allows digital images to be printed on photographic paper in mass quantities and is thereby ideally suited for commercial photograph production.
The principal object of the present invention is to provide a method and apparatus for creating a digital image on photographic paper and subsequent correction of color.
Another object of the invention is to provide a digital image printer that is capable of rapidly producing digital images on photographic paper having good clarity and sharpness and correct color content.
Another, more particular object of the invention is to provide a digital image printer having a modular controllable digital image component that is easily removed from the digital image printer and that may be coupled with conventional photograph printers.
Another, more particular object of the invention is to provide a modular removable digital image component that presents a complete image against the photographic paper without the use of a filter wheel or multiple light/filter source.